1. Field of the Invention
The present invention relates to a display unit such as a level indicator for audio apparatuses.
2. Description of the Related Art
Most audio apparatuses such as a CD or a DAT and most video apparatuses such as a television set or a VTR are equipped with an indicator for indicating the level of an input signal. Such an indicator is composed of an element such as a light emitting diode array or a liquid crystal indicator, and changes the number of displayed segments in accordance with the input level.
FIG. 5 shows an example of such an indicator. The indicator is provided with liquid crystal indicators 11-1 to 11-7, each of which is composed of a plurality of liquid crystal segments. The liquid crystal indicators 11-1 to 11-6 indicate the level of input signals in six frequency bands, and the liquid crystal indicator 11-7 indicates the average input level.
In this type of indicator, when a signal of a higher level than the current level is input, all the segment lamps below this level are immediately lit in correspondence with the input level, but when no signal of a higher level than the current level is input within a predetermined time, the segment lamps are sequentially turned off every predetermined time period so as to gradually lower the displayed level. This is called recovery control, which is carried out because if the level is lowered immediately after a signal is input, the eyes of the user cannot follow the change and cannot recognize the preceding displayed level.
Such a display including recovery control is applied to not only audio apparatuses but also various other apparatuses including electronic measuring instruments and the display panel of an automobile for displaying the number of revolutions of the engine, the vehicle's speed, etc. The recovery time is conventionally controlled by fixed hardware. In other words, a filter composed of a resistor R and a capacitor C is externally attached to an integrated circuit chip for controlling a liquid crystal indicator, and the recovery time is set by approximately selecting the values of the capacitor C and the resistor R.
Since the recovery time for the display is set by the filter composed of the capacitor C and the resistor R in a conventional level indicator, as described above, for example, the level indicator for seven frequency bands shown in FIG. 5 requires more than 20 parts. That is, the number of parts for external attachment is inconveniently very large. Especially, in the case of setting a long recovery time, the value of the capacitor C must be set at a large value, which leads to an increase in cost. If the values of the parts such as the capacitor C and the resistor R are not uniform, the values of the products also become non-uniform, so that it is difficult to set the recovery time of a product at the target value. If the deviation from the target value is too large, the adjusting process for correcting the deviation is necessary, which further increases the cost.
In addition, in the case of changing the recovery time due to a change in the specification of a product, it is necessary to change the value of each part to an appropriate value in correspondence with the changed recovery time, thereby requiring a lot of labor in manufacturing the product.